This invention concerns the use of a preservative in a hematological reference calibrator composition for instrumentation which determines hematological values in blood samples.
It is common medical diagnostic procedure to analyze and test the blood sample of a patient in order to make certain classic determinations with respect to the blood sample. This procedure is an important aid to the physician. The characteristic parameters to be determined are red blood count (RBC), white blood count (WBC), hematocrit (HCT), hemoglobin (Hgb), mean corpuscular volume (MCH), and mean corpuscular hemoglobin concentration (MCHC). Coulter Electronics, Inc. of Hialeah, Florida and other manufacturers sell several models of blood cell counting and analyzing instruments which are well known in the art. Instruments are sold which will accept a patient's blood sample and process the same sample automatically and continuously to provide one or more of the aforesaid parameters.
The general procedure of such instruments is to add a lysing agent to a suspension of dilute whole blood containing an anticoagulant. The lysing agent destroys the red blood cells and releases their content into solution. This resulting suspension has the coloring matter produced by the broken red cells and the unaffected white cells. A reagent is added to fix the hemoglobin in solution so that the color will be retained and made available for measurement of hemoglobin.
Prior to the use of automated equipment for the purpose of in vitro diagnostic testing of blood samples, calibration of the instrument is required depending on the design and degree of automation of the equipment. A calibrator composition, similar in nature to that of the blood sample which is routinely encountered by the user, is developed which is thoroughly evaluated against the instrument which has been calibrated by reference procedures. This calibrator, which has been provided with an assigned value, is offered to the user in order that he may calibrate his instrument to the assigned value with speed and accuracy.
As to be expected, a hematological composition for use in such a calibrator is prone to bacterial and fungal contamination. Therefore, a suitable preservative agent needs to be added. The typical sterility maintaining substances used in hematology were found to cause side effects, or otherwise not perform suitably for this purpose.
The preservative must be compatible with the blood sample which has been lysed as heretofore mentioned, and the preservative properties of the agent must not be reduced markedly because of the blood protein present. Likewise the antibacterial agent must not form pigments with the blood hemolysate or with other agents to be added later to make the hemoglobin determination. In addition, it must not form a gel which would interfere with keeping the hemolysate in a liquid state for the limited time in which the calibrator is in use, suitably for about 120 days at 4.degree. C.
The preservative must be sufficiently soluble in the hemolysate at the pH resulting from the concentration and amounts of the particular lysing agent used to provide a preservative amount of the agent against bacteria commonly found in the environment, and especially against Pseudomonas aeruginosa which is commonly found in the environment.